1. Field of the Invention
The present invention relates to a self-locking device for a table elevating screw, with which a nut of the screw is prevented from dropping down when a power associated is removed or disappeared.
2. Description of the Prior Art
Lifting and lowering operations are generally involved in mechanical devices. For the most part, the lifting and lowering operations are achieved pneumatically and hydraulically for the current mechanical devices. However, since the pneumatic and hydraulic mechanisms are susceptible to the physical factors of pressure and temperature, the objects lifted and lowered are difficult to be well positioned, apt to shift, and moved without good self-locking result, fine precision and proper reliability. Further, such pneumatic and hydraulic mechanisms are difficult to be designed. The pneumatic and hydraulic mechanisms can only provide a vertical positioning operation and require various peripheral elements and components for maintenance use. Accordingly, the pneumatic and hydraulic mechanisms cannot provide a good and convenient lifting and lowering operation.
In a hoist or an elevator, a braking or self-locking device has to be provided for the screw in prevention of dropping down of the nut of the screw when a power associated is removed or disappeared.
In the U.S. pat. No. 2,804,053, an actuator was disclosed, which comprises a hydraulic cylinder, a piston, a screw and a braking assembly. Hydraulic oil is instilled from an upper hydraulic entrance and a lower hydraulic entrance so as to cause the piston to ascend and descend. Meanwhile, the vertical movement of the piston also brings the screw to rotate. The braking assembly provides a braking operation by the hydraulic pressure. When the actuator is in a stop state, the braking assembly is operated to be in a locking state. When the actuator is ready to move, the braking assembly is operated to be in a release state. However, complex peripheral devices are required to control the hydraulic system to have a self-locking result.
In view of the above demerits encountered in the prior art, the inventors sets forth a simple and precise self-locking device, with which the issues of difficult positioning, inconvenient installation and poor self-locking performance can be successfully overcome, effectively promoting convenience and use of the mechanical lifting and lowering mechanisms.